Preheat oven and butter a 12-cup Bundt pan.

Combine the flour, baking soda, and salt in a medium mixing bowl.
Combine the butter, chocolate, and espresso in a medium saucepan. Stir over low heat until the chocolate and butter have melted.
Remove the pan from heat.
Add the sugar and bourbon and stir with a whisk until the sugar has dissolved and the mixture is smooth.
Place the eggs and vanilla in a large mixing bowl and mix with a wooden spoon or electric mixer on low speed. Gradually beat in the chocolate mixture.
Add the flour mixture and stir. Pour the batter into the prepared pan and smooth the top with a rubber spatula.
Bake until a toothpick inserted in the center of the Mississipi Mud Bundt Cake comes out clean.
Let the cake cool in the pan for about 5 minutes, invert it onto a wire rack, and then turn it right side up on a rack to cool completely.

Turn the cake out onto a wire rack set over a baking sheet.
Drizzle the glaze over the cake, allowing to run down the sides.
Let the glaze set for 30 minutes.

Espresso-Bourbon Glaze

Stir the butter, brown sugar, and espresso powder together in a small saucepan over medium heat until the butter melts.
Stir in the heavy cream. Simmer for 1 minute.
Remove from the heat. Gradually add the confectioner’s sugar, whisking until smooth.
Mix in the bourbon.
Let the glaze cool slightly before using.